Transformer controlled chargedparticle accelerator



June 25, 1968 ABRAMYAN ET AL 3,390,303

TRANSFORMER CONTROLLED CHARGED-PARTICLE ACCELERATOR Filed Aug. 6, 1965 5 Sheets-Sheet 1 FIG. 1

June 25, 1968 E, ABRAMYAN ET AL 3,390,303

TRANSFORMER CONTROLLED CHARGED-PARTICLE ACCELERATOR Filed Aug. 6, 1965 5 Sheets-Sheet 2 FIG. 2 4 I L,

FIG. 50

2/ F/G. 6 N E e FIG. 3

June 25, 1968 ABRAMYAN ET AL 3,390,303

TRANSFORMER CONTROLLED CHARGED-PARTICLE ACCELERATOR Filed Aug. 6, 1965 5 h heet 3 United States Patent Oflice Patented June 25, 168

3,390,303 TRANSFORMER CONTROLLED CHARGED- PARTTCLE ACCELERATOR Evgeny Aramovich Abramyan, ul. Tereshkovoi 15, kv. 1, and Vasily Alexandrovich Gaponov, Zolotodolinskaya ul., 9 kv. 27, both of Novosibirsk, U.S.S.R.

Filed Aug. 6, 1965, Ser. No. 477,841 4 Claims. (Cl. 315-57) ABSTRACT OF THE DISCLOSURE A charged-particle accelerator in which there is an accelerating tube with an injector and control grid, there being a transformer with primary and secondary windings, the latter providing an acceleration voltage in the tube, the transformer having a core divided into insulated sections, an oscillating circuit being used to insure a constant gradient of voltage along said tube.

The present invention relates to units adapted for accelerating charged particles up to the energy of several mev., featuring high efiiciency and making possible the production of high-power particle beams.

The charged-particle accelerator known in the art comprises an accelerating tube and a transformer which insures constant voltage across the accelerating tube. The transformer core is divided into sections insulated from each other, the secondary winding being wound thereon. T rectify the voltage fed to the accelerating tube, the turns of each section are provided with a rectifier and a capacitor.

The disadvantage of such charged-particle accelerators is the necessity of operating at a frequency of the order of 1000 c.p.s., i.e., much in excess of the power frequency which fact imposes stringent requirements to be met by the material the core is made of. Another disadvantage is the complexity of the accelerator design which incorporates a large number of valves and a converter to feed the primary winding of the transformer.

It is an object of the present invention to provide a charged-particle accelerator capable of accelerating particles up to the energy of several mev., the power in the particle beam being as high as dozens of kw.

Another object of the invention is to provide a chargedparticle accelerator operating at a power frequency, i.e., 50-60 c.p.s.

Still another object of the invention is to provide a charged-particle accelerator featuring high (9S98 percent) efficiency.

Yet another object of the invention is to provide a charged-particle accelerator having the energy stability of 1 percent and better.

In accordance with said and other objects the present invention consists in a charged-particle accelerator which comprises an accelerating tube, a transformer with a core divided into sections insulated from each other, a device for stabilizing the voltage across the accelerating tube by means of controlling the tube current preferably with the help of a control grid in the tube injector, and an oscillatory circuit arranged at the high-voltage end of the secondary winding of the transformer and providing for the constancy of the potential gradient along the secondary winding and the accelerating tube.

Besides, when operating with a high-power beam, in order to increase the electric strength and prolong the service life of the accelerator, screens are mounted in the accelerating tube, said screens being preferably made of a heavy metal and serving to confine the radiation propagation region. The relation of the value of the insulation gap between the transformer sections to the height of the section is chosen to correspond to the maximum Q-factor of the transformer.

To accelerate the particles by the charge exchange technique up to the energy exceeding the maximum voltage across the secondary Winding of the transformer, the secondary winding can be made of two parts whose turns are wound in opposite directions. Both terminals of the secondary winding are then grounded, and the voltage at the central point of the winding is maximum.

Other objects and advantages of the present invention will become apparent from a description presented hereinbelow and the accompanying drawings, wherein:

FIG. 1 diagrammatically shows a cross sectional view of the charged-particle accelerator of the invention;

FIG. 2 shows an equivalent electric circuit of the magnetic circuit of the transformer with the secondary winding;

FIG. 3 shows a portion of the accelerating tube with screens;

FIG. 4 shows an equivalent electric circuit of the transformer;

FIG. 5a is a voltage curve at the primary winding of the transformer;

FIGS. 51), c and d show the voltage and current curves of the accelerating tube at various duties of the chargedparticle accelerator;

FIG. 6 is a wiring diagram showing the way six charged-particle accelerators, conventionally denoted as valves, should be connected to three-phase mains;

FIG. 7 is a diagrammatic sectional view of the chargedparticle accelerator in which the secondary winding of the transformer is made of two parts.

The charged-particle accelerator of the invention is provided with a transformer which comprises magnetic circuit 1 (FIG. 1) with core 2, primary winding 3 and secondary Winding 4. The magnetic circuit and the core are made of conventional transformer steel. Core 2 is divided into sections 5 insulated from each other and fixed on insulators 6.

Primary winding 3 of the transformer is made in the form of a coil with screen 7. Secondary winding 4 is constituted by series-connected coils 8. Each section 5 supports two coils, and the central point of the pair of coils is electrically connected with the section. The number of turns in the secondary winding of the transformer and the dimensions of the transformer are so selected that the natural frequency of the transformer accelerator is close to the power frequency (i.e., 5060 c.p.s.).

To insure equal voltage at all coils 8, the charged particle accelerator is provided with an oscillatory circuit which incorporates inductance coil 9 and a lumped capacitance, viz, capacitor 10. Coil 9 is a part of the secondary winding. The number of ampere turns in coil 9 is selected in accordance with the value of the reluctance of highvoltage gap 11, in which a maximum voltage electric field is set up by the windings of the transformer. Gap 11 is capable of withstanding the voltage produced by the secondary winding of the accelerator transformer.

In the equivalent electric circuit shown in FIG. 2, the magnetic resistance of gap 11 is denoted by resistor 12. Resistors 13 stand for the magnetic resistances of -each gap between sections 5 of the transformer core (FIG. 1).

The ampere turns of every two coils 8 mounted on one section 5 are equivalent to the electromotive forces of voltage sources 14-. The ampere turns of coil 9 are equivalent to the electro-motive force of voltage source 15.

The use of the oscillatory circuit makes it possible to considerably reduce spurious fluctuations of voltage across coil 8 of the secondary winding of the transformer.

The Q-factor WL/ (R) of the transformer is chosen to be maximum, which is achieved by selecting the optimum a value of the gap between the core sections. It can be easily shown that the Q-factor of the magnetic circuit of the transformer has a maximum depending on the relation 1 /1 where I is the size of the gap between the core sections and I is the section height. The Q-factor (otherwise the ratio of the reactive power to losses power) is the quality factor of the accelerator during idle run and it is the reverse of the losses. The accelerator is characterized by minimum losses.

Accelerating tube 16 is disposed inside the transformer core and connected with sections of the core to provide a constant potential gradient at the tube. The inclination of electrodes 17 to the axis of the tube can be varied. Shown in FIG. 3 are electrodes 17 with variable inclination.

To protect insulation rings 18 of the tube, sections 5 of the transformer core, as well as other parts and the space of the charged-particle accelerator from radiation, screens 18' are provided in the accelerating tube, e.g. of conical form, made of lead or another, preferably heavy, metal, said screens completely enveloping the region where the charged particles are traveling. Such screening is particularly imperative when a high-power beam is passed along the accelerating tube, since in this case there arises a considerable Xrad'iation in the region close to the axis of the tube.

Injector 19 (FIG. 1) of the tube is disposed at the highvoltage end of the tube and is provided with control grid 19'. To control the value of the tube current any other element fit for the purpose can be used instead of the grid.

In the equivalent elctric circuit of the transformer (FIG. 4) inductance coil 20 is equivalent to the secondary winding of the transformer, capacitor 21 is equivalent to the distributed capacitance of the accelerator, resistor 22 is equivalent to the resistance of the accelerating tube, and inductance coil 23 is equivalent to the leakage inductance of the primary winding of the transformer.

The charged-particle accelerator can be operative at various levels or various duty cycles when accelerating charged particles of similar sign.

Feeding voltage U (FIG. 5a) is supplied to the pri iary winding of the transformer. If the injector is cut in all the time and the control grid is not at cut-off, then the current passes through the accelerating tube during half a period. The value of current i (FIG. 5b) of the tube is determined by the extraction potential and maximum current of the injector.

More often is the case when the injector is open only for a period of time T1, during which the accelerating voltage charges but insignificantly (by to percent depending upon the task the accelerator is to fulfill).

Most interesting is the case when the tube current is controlled.

Voltage stabilizing device 24- with a feedback, which stabilizes the voltage at the accelerating tube (FIG. 1), controls the current of injector 19 in such a way that there is provided a partial voltage drop at inductance coil 23 which corresponds to the leakage inductance of the primary winding (FIG. 4), voltage U at the tube being maintained constant (a sine curve is shown in 5d in broken line). The energy of particles during the pulse may be made constant with an accuracy of at 1 percent and better.

To stabilize the voltage at the accelerating tube use can be made not only of the leakage inductance of the primary winding of the transformer, but also of the inductance of the coil disposed individually of the transformer.

To load the mains more uniformly, i.e. to employ both voltage half periods, the accelerating tube can be provided with two sources of particles simultaneously, i.e. with a source of electrons and a source of positive ions. The same effect can be obtained with two charged-particle accelerators operated in parallel in each phase of the feeding voltage. The connection diagram for six chargedparticle accelerators to operate from three-phase mains is shown in FIG. 6, said accelerators being conventionally designated as valves 25.

Voltage stabilizing device 24, which stabilizes the volage at the accelerating tube, can be controlled remotely, whereby the time T or 1- during which the current passes, can be varied from zero to the value maximum for a given installation.

Thus, for the operation duty of the installation whose voltage and current curves are shown in FIG. 5d the value of T2 mm is of the order of A of the period of the feeding voltage U i.e. with the frequency of the feeding voltage being 50 cps. T2 =5 msec. Greater values of 7- correspond to greater current values and an average energy in the particle beam.

In case it is necessary to obtain the energy of particles varying with time 7'2 in accordance with the preset law, voltage stabilizing device 24, which stabilizes the voltage at the accelerating tube, can be provided with a programming device (not shown).

The transformer together with the accelerating tube is placed into casing 26 (FIG. 1) filled with gas at a pressure of at least 10 atm. which provides for the required electric strength of the gaps.

In accordance with the invention, there is provided a method for controlling the spectrum of the energy of charged particles and an apparatus for accomplishing this method. The apparatus has been explained in the equivalent electric diagram of FIG. 4. Supplementing FIG. 4 is a more detailed diagram of the apparatus (FIG. 4a) in which resistance 22 used in place of an accelerating tube has been replaced by a diagram of the accelerating tube having a control electrode grid 19'.

The system for controlling the spectrum of the energy of charged particles comprises, apart from reactive and active elements, dissipation inductors of transformer 23, which serve primarily to vary the voltage drop in response to changes in the current flowing through the accelerating tube, voltage meter 30 (capacitive transducer) on accelerating tube 22 and bias voltage source 31, the signals from which are supplied to comparison circuit 32, and amplification unit 33, whose input is connected with measuring circuit 32 and the output with control electrode grid 19' of accelerating tube 22.

The above-described feedback circuit is used to vary the electron current (flow of charged particles) flowing through the accelerating tube and causing such variations in the voltage drop across the reactive and active elements of the accelerator as are required by the voltagevariation law established by programmer 31 (FIG. 4a) for the accelerating tube.

The specific construction of each unit of the system for controlling the spectrum of the energy of charged particles is not shown, since they can be constructed with the help of standard elements on common principles known to any engineer skilled in the field.

The circuit described above is a more detailed representation of device 24 mentioned in line 55 of column 3.

The claimed control system permits operation of the accelerator under various conditions. The application recites three variants (FIG. 5) as examples. The graph in FIG. 5b shows a variant in which control system 24 (FIG. 1) keeps electron injector 19 constantly in open state; FIG. 5c illustrates a case when control system 24 opens injector 19 for the time T; and in FIG. 5d-the case when system 24 maintains a constant voltage across the accelerating tube throughout the length of the current pulse, i.e., it helps obtain a monochromatic electron beam.

Other operating conditions include continuous control of the voltage across the accelerating tube to maintain the present spectrum of the energy of accelerated particles. This is readily understood from the above description of the control system and from FIG. 4a.

Though the present invention has been described in connection with the preferred embodiment thereof, it is to be understood that various changes and modifications may be made without departing from the spirit and scope of the invention as those skilled in the art will easily understand.

Such changes and modifications are considered as falling within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A charged-particle accelerator comprising an accelerating tube, an injector in said tube and including a control grid; a transformer including a core divided into sections insulated from each other, said transformer including primary and secondary windings and creating an accelerating electric field in said accelerating tube; means for stabilizing the voltage at said accelerating tube by controlling the current of the tube; and an oscillatory circuit means coupled to the secondary winding of said transformer and insuring a constant potential gradient along said secondary winding of the transformer and along said accelerating tube.

2. A charged-particle accelerator comprising an accelerating tube including screens of heavy metal limiting the radiation propagation region, an injector in said tube including a control grid; a transformer including a core divider into sections insulated from each other, said transformer including primary and secondary windings and creating an accelerating electric field in said accelerating tube; means for stabilizing the voltage at said accelerating tube by controlling the current of the tube; and an oscillatory circuit means disposed at the high-voltage end of the secondary winding of said transformer and insuring a constant potential gradient along said secondary winding of the transformer and along said accelerating tube.

3. A charged-particle accelerator comprising an accelerating tube, an injector in said tube and including a control grid; a transformer including a core divided into sections insulated from each other and separated by gaps therebetween, said transformer including primary and secondary windings and creating an accelerating electric field in said accelerating tube, the relation between the size of the gaps between said transformer sections and the height of the core being such as to correspond to the maximum Q-factor of the transformer; means for stabilizing the voltage at said accelerating tube; and an oscillatory circuit means disposed at the high-voltage end of the secondary winding of said transformer and insuring a constant potential gradient along said secondary winding of the transformer and along said accelerating tube.

4. A charged-particle accelerator comprising an accelerating tube, an injector in said tube and including a control grid; a transformer including primary and secondary windings and creating an accelerating electric field in said accelerating tube, the core of said transformer being divided into sections insulated from each other and the secondary winding thereof including two parts including turns wound in opposite directions, said secondary winding including terminals at ground potential and a center tap under a maximum voltage; means for stabilizing the voltage at the accelerating tube by controlling the current of said tube; and an oscillatory circuit means disposed on the portion of the secondary winding of the transformer under maximum voltage, said oscillatory circuit means insuring a constant potential gradient along said secondary winding of the transformer and said accelerating tube.

References Cited UNITED STATES PATENTS 2,762,941 9/1956 Turner 31363 2,820,142 1/1958 Kelliher 313-63 2,856,532 10/1958 Martina 3l363 2,922,905 1/1960 Van DeGraaft 31363 DAVID J. GALVIN, Primary Examiner. 

